FIELD ON THE INVENTION
The invention relates to the manufacture of images which provide a visual impression of three-dimensional depth. More particularly, the invention is related to laminating a lineiform image sheet to a lenticular array sheet using a radiation-curable adhesive.
Lenticular arrays or sheets are a known means for giving certain images the appearance of depth. Images are created which comprise an array of parallel image lines which form a composite picture or lineiform image of a scene viewed from different angles. A lenticular sheet comprising an array of contiguous, parallel, elongated lenticules is positioned in front of the lineiform image, so that the lenticules cause each eye of the viewer to see different elements or views of the overall image. Thus, the viewer will interpret the result as depth of field. Depth images of this type have been created by exposing a photographic film through a lenticular array sheet and then developing the latent image. If the lenticular array is bonded to the photographic medium before exposure, then the lineiform image and the array are automatically aligned. These types of images generally are not of high three-dimensional quality and do not lend themselves to electronic image manipulation before the print is finalized.
Commonly assigned U.S. Pat. No. 5,276,478 describes an improved apparatus and methods for making depth images in which the lineiform image is formed electronically, the spacing between image lines being controlled to provide improved alignment with the lenticules of a lenticular array sheet. A recorded image sheet or medium bearing a lineiform image suitable for viewing by either transmitted or reflected light contains sets of image lines that are produced optically or electronically to provide the composite lineiform image. The image sheet typically is rather thin and quite flexible but may be stiff or rigid. A very thin layer of adhesive, typically a contact adhesive provided on the back side of a lenticular array sheet or on the surface of the image sheet, joins the image and array sheets at their smooth, interfaced surfaces. The lenticular array sheet may be made from a suitable flexible plastic and typically has a thickness of about 0.05 inch (1.27 mm). For best effect, the parallel lenticules of the array sheet must be positioned with one lenticule for each set of image lines. When viewed, one image line of each set is viewed by each eye of the observer, so that the observed lines merge to create a complete scene with perceived depth of field. The eyes see the image via light rays through lenticules as a series of simultaneous image lines or view slices. The scenes provided by the first and second views provide the depth perspective.
While such depth image systems are capable of displaying images with striking appearances of three dimensions, efficiency of production and the quality of the image seen by the observer are dependent greatly on defect-free lamination of the image and array sheets and on quick, accurate alignment of the image lines and the lenticules. When contact or pressure sensitive adhesive is used between the two sheets, achieving accurate alignment can be quite difficult, particularly for rather large images. Other adhesives such as hot melts, two-part epoxies and heat-reactive adhesives have been used with mixed success. Such adhesives often are too viscous or bond instantly on contact and prevent the sheets from being properly laminated and accurately aligned. Some adhesives cure too slowly for efficient production use. Variations in the thickness of the adhesive layer also have led to dimensional distortions and poor alignment between the image sheet and the lenticular sheet. Some adhesives impart heat or stress to the sheets which can cause permanent distortion of the viewed image. Regardless of the type of adhesive used, bubbles of air can become trapped between the sheets during lamination, thus leading to defects in the final image. Variations in thickness of the array sheets can contribute to entrapment of air between the sheets during lamination, since the array sheet may not fully contact the image sheet in the lamination nip. Also, providing and maintaining correct alignment of the sheets during curing of the adhesive has been difficult to accomplish using known techniques for assembling depth images.
Commonly assigned co-pending application, Ser. No. 278,436, filed Jul. 21, 1994, describes a method and apparatus useful for assembling or laminating a depth image from an image sheet bearing a lineiform image and a lenticular array sheet having lenticules parallel to the lineiform image and a layer of adhesive between the image and array sheets.
Once alignment has been achieved, means are provided for curing the adhesive to ensure permanent alignment of the array and image. The adhesive may be curable by ultraviolet light, so that the means for curing comprises a source of ultraviolet light. The ultraviolet light may be directed through the array sheet or may be transmitted through the image sheet. The source of ultraviolet light may have a longitudinal axis essentially parallel to the lenticules, and the apparatus may include means for moving the vacuum platen and the means for gripping past the ultraviolet light source. The means for curing alternatively may comprise an electron beam source.
There is a need for an improved adhesive that provides optical clarity, controlled viscosity, and substantially instant cure on demand.